Axial piston pump

ABSTRACT

The invention relates to an axial piston pump, particularly for hydraulic systems, comprising a cylinder drum ( 1 ) which can be rotationally driven about an axis ( 15 ) in a pump housing ( 7 ), and in which piston cylinder units are arranged in a circle at an offset, said pistons ( 21 ) being at least indirectly supported on a swashplate ( 3 ) by their actuation end ( 31 ) which is accessible outside the cylinder drum ( 1 ). Between the swept volumes ( 19 ) of the piston cylinder units and a stationary fluid inlet and stationary fluid outlet of the pump housing ( 7 ), a control device ( 23 ) is arranged which comprises fluid channels ( 25, 26 ) for the targeted transfer of fluid from the fluid inlet into the swept volumes ( 19 ) and from said swept volumes ( 19 ) to the fluid outlet. The invention is characterised in that at least one pressure compensation channel ( 28, 30 ) is provided in the control device ( 23 ), between said fluid channels ( 25, 26 ), in order to build or release fluid pressure in the swept volumes ( 19 ) in a targeted manner.

The invention relates to an axial piston pump, in particular for hydraulic systems, having a drivable cylinder drum, rotating around an axis in a pump housing, in which the piston-cylinder units are arranged on a circle at an offset, wherein the pistons are supported, at least indirectly, on a swash plate at their actuating ends, which is accessible from outside the cylinder drum, and a controlling device is disposed between the swept volumes of the piston-cylinder units and a stationary fluid inlet and a stationary fluid discharge of the pump housing, the controlling device having fluid channels for the targeted transfer of fluid from the fluid inlet into the swept volumes and from the swept volumes to the fluid discharge.

Axial piston pumps of this type represent the prior art. They are commonly used for the pressure medium supply to loads, such as operating cylinders, hydraulic motors, and the like. Axial piston pumps of the aforementioned type, in which the inclination of the swash plate relative to the axis is adjustable, distinguish themselves from likewise known axial piston pumps with a fixed swash plate by a better energy balance in their operation. While pumps with a fixed swash plate, as fixed displacement pumps, always deliver a constant flow rate of the fluid at a given drive speed even when no power is requested by fluid-operated units and therefore the flow resistances in the hydraulic circuit must be overcome even during idle running, expending drive energy that provides no useful energy, the delivery volume can be set to zero and the requirement for driving energy can be minimized through the adjustment of the swash plate inclination. An axial piston pump of this type is disclosed in DE 44 15 510 C1. Due to the successive strokes the pistons perform during operation, the pressure generated is not free from pressure pulsations even if a larger number of piston-cylinder units is housed in the cylinder drum. When using such pumps, it is therefore necessary in some cases to provide measures for smoothing pressure pulses, for example in the form of pulsation dampers.

With regard to this difficulty, the invention addresses the problem of providing an axial piston pump that distinguishes itself with a comparatively smoother pressure course.

According to the invention, this problem is solved by an axial piston pump having the features of Claim 1 in its entirety.

According to the characterizing part of Claim 1, an essential feature of the invention is that at least one pressure equalization channel is provided in the controlling device between the fluid channels for selectively establishing or releasing fluid pressure in the swept volumes. This opens up the possibility of minimizing pressure surges in the overflow of the control edges between cylinders and the pressure-side and suction-side fluid channels by initiating a corresponding pressure build-up via a pressure compensating channel before reaching a pressure-side fluid channel or initiating a pressure reduction via a compensating channel before reaching a suction-side fluid channel. In particular, this pressure build-up in the area of the transfer from the suction side to pressure side occurs more gently.

Preferably the arrangement is devised such that only one swept volume each is connectable with a high pressure source via the respective pressure compensating channel, wherein the high pressure source can be, for example, at least one compression chamber. Such a chamber may be integrated, for example, into the lower housing part of the pump housing, with which the controlling device comprising the fluid channels is connected.

Particularly advantageously, the respective pressure compensation channel can be arranged such that the connection to the respective swept volume can only be established after the connection from the fluid inlet to this swept volume is closed.

Furthermore, the pressure compensation channel can be arranged such that the connection from it to the respective swept volume is can be closed only after the connection from the fluid discharge to this swept volume is established.

For a targeted pressure release before the establishment of a connection of the respective swept volume space to the suction-side fluid channel, a second pressure compensation channel may be provided, by means of which only one swept volume at a time can be connected to a pressure sink. This may be a tank that is part of an associated drainage system.

The pressure compensation channel leading to the pressure sink can be arranged such that the connection to the respective swept volume can be established only after the connection from the fluid discharge to this swept volume is closed.

With regard to the arrangement of this second pressure compensating channel, the arrangement can be made such that its connection from it to the respective swept volume can be established only after the connection of the fluid discharge to this swept volume is closed and such that the connection to the respective swept volume is closable only after the connection from the fluid inlet to this swept volume is established.

In particularly preferred embodiments, the controlling device comprises a stationary control disk, which preferably forms a floor for the swept volumes of the rotating piston-cylinder units, wherein the control disk preferably further comprises kidney-shaped fluid channels for the establishment of connections to the piston-cylinder units.

In such embodiments, at least one pressure compensating channel is provided in the form of a bore in the control disk.

The control disk may be disposed on a connecting plate formed on the lower housing part of the pump housing, wherein the respective compression chamber is provided in the connecting plate and a connecting channel is provided from the compression chamber to the corresponding pressure compensating channel.

Preferably, the respective compression chamber is closed by a screw plug.

Below the invention is explained in detail with reference to the drawing. In the figures:

FIG. 1 shows a longitudinal section of an axial piston pump according to one embodiment of the invention;

FIG. 2 is a partially cutaway oblique perspective view of the lower housing part of the embodiment of FIG. 1, with view on the control disk fixed to the connection plate of the lower housing part;

FIG. 3 is an oblique perspective view of the separately shown control disk; and

FIGS. 4 to 6 are schematic functional diagrams to illustrate the operation of the axial piston pump according to the invention.

FIG. 1 shows an embodiment of the axial piston pump according to the invention with a swash plate design. In the manner common for axial piston pumps of this type, a rotatably drivable cylindrical drum 1 is provided in a pump housing 7 with a corresponding swash plate 3, which is pivotable for adjustment of the flow rate, and thus the system pressure that can be generated by the pump, wherein the pivot axis of the swash plate 3 in FIG. 1 is designated by 37. The pump housing 7 comprises an upper part 9, shown at the top in the drawing, and a lower part 11. A drive shaft 13 for the cylinder drum 1 is mounted in the upper part 9 in a tapered roller bearing 16 and in the lower part 11 by means of a slide bearing 17 for rotation about the axis designated by 15. The cylinder chambers 19 of the cylinder drum 1, having a piston 21 guided therein (in the section plane of FIG. 1, only one cylinder chamber 19 is visible), are in contact with a control plate 23 on the end of the cylinder shown at the bottom in the drawing, wherein the control plate is in contact with the lower housing part 11. The control plate 23 comprises control openings of fluid channels 25 and 26 for the connections between a suction-side connection 27 and a pressure-side connection 29 into the cylinder chambers 19 of the cylinder drum 1. On the side located at the top in the drawing, facing the cylinder drum 1, the control plate 23, which is shown separately in FIGS. 2 and 7, is provided with a coating 24, see FIG. 2, which is produced by the process according to the invention and forms the bearing surface on which the slightly concave, curved bottom surface 8 of the cylinder drum 1 slides during its rotational movement. In FIG. 1, portions of the coating 24 that form the bearing points between a central passage 14 and adjacent control openings of fluid channels 25 and 26 are designated by 6.

During the movement of the cylinder drum 1, the pistons 21 slide across a respective sliding block 31 on the sliding surface 33, which is located on the bottom side of the swash plate 3. The sliding blocks 31 are connected with the piston top side of the corresponding piston 21 in the manner of a ball joint, wherein the ball joint is formed by a ball head 34 on the piston 21 and a ball socket 36 in the sliding block 31. The ball joint is secured by means of a crimp 38 on the sliding block 31. Oil holes 35 in the ball head 34 and sliding block 31 provide access for fluids, such as hydraulic oil, for the lubrication of the sliding surface 33. Similar to the control plate 23, the sliding blocks 31 also comprise a coating 24 produced by the process according to the invention.

As mentioned above, the swash plate 3 is adjustable about the pivot axis 37, which lies in the plane of the sliding surface 33 of the swash plate 3, for setting the delivery volume. This pivot axis 37 is defined by the swash plate bearing formed between the swash plate 3 and the upper part 9. It comprises a plastic bearing shell 39 on the upper part 9, on which the swash plate 3 is guided with a dome-shaped sliding surface 41. In the sliding surface 41, an upwardly conically flared opening 43 is formed in the swash plate 3 for the passage of the drive shaft 13. On both sides next to the opening 43, guide rails 45 protruding from the sliding surface 41 are provided as part of the swash plate bearing. For the pivotal movement of the swash plate 3 about the pivot axis 37, the side of the swash plate 3 on the left in FIG. 1 is screwed to a pivot lever 47, which extends parallel to the axis 15 next to the cylinder drum 1 and which, on its end at the bottom in FIG. 1, is movable in the direction perpendicular to the drawing plane in order to effect a corresponding pivotal movement of the swash plate 3 about the pivot axis 37. The pivot lever 47 is screwed to the corresponding side of the swash plate 3 with an internal thread located in a drilled hole 51.

A joint tube 5 which forms part of a feeding and pressing device, is arranged laterally next to the cylinder drum 1 in a direction parallel to the axis 15, as shown in FIG. 1. At its end at the bottom in FIG. 1, the joint tube 5 is mounted in a seat 53 in a connection block 55 on the lower housing part 11, wherein the receptacle 53 allows an axial displacement of the joint tube 5. The block 55 comprises a connection channel, not visible in FIG. 1, to the pressure side 29, which opens into the receptacle 53 of the joint tube 5. The upper end of the joint tube 5 is hinged to the swash plate 3 via a connecting piece 58 which is disposed laterally outside the sliding surface 33 on the bottom side of the swash plate 3. The joint connection is implemented by a type of ball joint and comprises a ball head 59 at the upper end of the joint tube 5, which is mounted in a ball socket 61 of the connection piece 58. The joint tube 5 is braced against the swash plate 3 via the connecting piece 58. For this purpose, a laminated disk spring 63 is disposed between the lower end of the joint tube 5 and the bottom of the receptacle 53. A fluid passage 67 in the connecting piece 58 continues the fluid connection to the pressure side 29 through the tube opening on the ball head 59 and to the swash plate. 3. The passage 67 of the connecting piece 58 is followed by lubrication channels 73, 75 formed in the swash plate 3, only some of which are visible in FIG. 1 and the vertical channels 75 of which open into points of the sliding surface 41 suitable for the supply of lubricant to the swash plate mounting.

FIG. 2 shows the lower housing part 11 in an orientation in which the control plate 23 attached to the top part and the lateral connection of the pressure side 29 are visible. On the side of the lower housing part 11 shown at the top in FIG. 2, two cylindrical compression chambers 18, integrated into the housing wall, are provided which are closed with screw plugs 12 and are in connection with connecting holes 20 and 22 at their inner end. A pressure compensating channel 28 opens into the latter in the form of a narrow compression chamber bore, which is formed in the control disk 23. Approximately opposite of the compression chamber bore 28, another pressure compensation channel 30 is formed in the control disk 23 in the form of a relief hole, which also has a small cross section. At the end of the kidney-shaped fluid channel 25 adjacent to the relief hole 30, which is assigned to of the low pressure, or suction, side 27, the opening edge has a flat section, which forms a control notch 32. The function of the compression chamber bore 28, the relief hole 30, and the control notch 32 will be discussed below in further detail with reference to the FIGS. 4 to 6.

FIGS. 4 to 6 show the duty cycle for a single cylinder 19 of the cylinder drum 1 in the form of a functional diagram with the control disk 23 in a developed view, wherein the rotational direction is designated by arrows 40 and the direction of the piston stroke is designated by arrows 42. The upper dead point and lower dead point are designated by OT and UT. Corresponding to the direction of rotation designated by 40, FIG. 4 illustrates a process in which, when the piston 21 is at its top dead point, after the end of a suction process, the connection to the fluid channel 25 of the low-pressure side closes and then, cf. left side of FIG. 4, the compression chamber bore 28 opens. This initiates a pressure build-up in the volume of the cylinder 19 by supply from the compression chamber 18 even before the connection to the high-pressure side fluid passage 26 opens. This state after completion of the suction stroke of the piston 21 is shown on the left side in FIG. 5, where the connection to the high-pressure side fluid passage 26 is now opened, while, at the same time, the compression chamber 18 is still connected with the cylinder 19 via the compression chamber bore 28, so that the compression chamber 18 is now charged from the pressure-side fluid passage 26. In the further progress of the working cycle, as shown on the right side in FIG. 5, the delivery stroke of the piston 21 is carried out while the connection to the compression chamber 18 via the compression chamber bore 28 is already broken. The left side of FIG. 6 illustrates the situation in which, at the start of a suction stroke of the piston 21, the connection via the relief hole 30 to a tank 46, serving as a pressure sink, begins to open.

This results in the relief of residual pressure from the cylinder 19 before the connection with the low-pressure side fluid passage 25 is established, as shown on the right side in FIG. 6. More precisely, the connection to the low-pressure side fluid passage 25 is not established suddenly over the full cross-section of the fluid channel 25, but gently on the control notch 32, as shown on the right side in FIG. 6.

By connecting to the compression chamber 18, the pressure in the cylinder 19 is elevated from “suction pressure” to “working pressure” before the opening of the high-pressure side fluid passage 26 is achieved. For this purpose, pressure is obtained from the compression chamber 18. After achieving the connection to the high-pressure side fluid passage 26, it is connected with the compression chamber 18 via the cylinder volume and the compression chamber bore 28 so that the pressure in the compression chamber 18 is raised back to the existing operating pressure before the next piston 21 reaches the reversal region. In conjunction with the smooth transition, achieved by means of the control notch 32, and the previously effected pressure relief via the relief hole 30, cf. the situation shown on the left side in FIG. 6, the overall result is an optimized operational behavior with a minimum of pressure pulsations. 

1. An axial piston pump, in particular for hydraulic systems, having a drivable cylinder drum (1), rotating around an axle (15) in a pump housing (7), in which the piston-cylinder units are disposed on a circle at an offset, wherein the pistons (21) are supported, at least indirectly, on a swash plate (3) with their actuating ends (31), which are accessible from outside the cylinder drum (1), and a controlling device (23) is disposed between the swept volumes (19) of the piston-cylinder units and a stationary fluid inlet and a stationary fluid discharge of the connecting plate (11), the controlling device having fluid channels (25, 26) for the targeted transfer of fluid from the fluid inlet into the swept volumes (19) and from the swept volumes (19) to the fluid discharge, characterized in that at least one pressure compensation channel (28, 30) is provided in the controlling device (23) between the fluid channels (25, 26) for selectively establishing or relieving fluid pressure in the swept volumes (19).
 2. The axial piston pump according to claim 1, characterized in that only one swept volume (19) at a time can be connected to a high pressure source (18) by means of the respective pressure compensation channel (28).
 3. The axial piston pump according to claim 1, characterized in that the high-pressure source is at least one compression chamber (18).
 4. The axial piston pump according to claim 1, characterized in that the respective pressure compensation channel (28) is arranged such that the connection to the respective swept volume (19) can be established only after the connection from the fluid inlet (25) to this swept volume (19) is closed.
 5. The axial piston pump according to claim 1, characterized in that the pressure compensation channel (28) is arranged such that the connection from it to the respective swept volume (19) can be closed only after the connection from the fluid (26) discharge to this swept volume (19) is established.
 6. The axial piston pump according to claim 1, characterized in that a second pressure compensation channel (30) is provided, by means of which only one swept volume (19) at a time can be connected to a pressure sink (46).
 7. The axial piston pump according to claim 1, characterized in that the pressure sink is a tank (46).
 8. The axial piston pump according to claim 1, characterized in that the second pressure compensation channel (30) is arranged such that the connection from it to the respective swept volume (19) can be established only after the connection from the fluid (26) discharge to this swept volume (19) is closed.
 9. The axial piston pump according to claim 1, characterized in that the second pressure compensation channel (30) is arranged such that the connection from it to the respective swept volume (19) can be closed only after the connection from the fluid inlet (25) to this swept volume (19) is established.
 10. An axial piston pump according to claim 1, characterized in that the controlling device is a stationary control disk (23), which preferably forms a bottom for the swept volumes (19) of the rotating piston-cylinder units (1), wherein the control disk (23) preferably further comprises kidney-shaped fluid channels (25, 26) for the establishment of connections to the piston-cylinder units.
 11. The axial piston pump according to claim 1, characterized in that at least one pressure compensation channel is provided in the form of a drilled hole (28, 30) in the control disk (23).
 12. The axial piston pump according to claim 1, characterized in that the control disk (23) may be arranged on a connecting plate formed on a connecting plate of the housing (7), wherein the respective compression chamber (18) is provided in the connecting plate (11) and a connecting channel (20, 22) is provided from the compression chamber (18) to the corresponding pressure compensating channel (28).
 13. The axial piston pump according to claim 1, characterized in that the respective compression chamber (18) is closed by a screw plug (12). 